Adding routes via route attributes is a way of defining the route for every controller action as an attribute on top of controller action methods.

Within the controller class (in our case, HomeController), add the Route attribute before the Index method:

[Route("Home/Index")]
public IActionResult Index()
{
    return View();
}

This instructs ASP.NET Core MVC to pass requests to the Index method whenever the URL looks like http://example.com/Home/Index. As patterns are not supported in attribute routing, if we want to make the Index method of HomeController the default of the application, then we need to add multiple Route attribute calls on top of the Index method:

[Route("")]
[Route("Home")]
[Route("Home/Index")]
public IActionResult Index()
{
    return View();
}

Attribute routing makes it easier to add new routes and keep them up-to-date with name changes or architectural code changes, but it doesn't support complicated patterns and makes it harder to see the full route list of the application. Attribute routing is, in most cases, the preferred way for ASP.NET Core web APIs.